A method and apparatus for injecting one or more fluids into a borehole.
Boreholes such as producing wellbores may periodically require treatment in order to maximize the efficiency of the recovery of fluids from the borehole. Such treatments often involve the injection of treatment fluids into the borehole and thus into the formation surrounding the borehole.
The treatment fluids may serve a variety of purposes. For example, fluids may be injected into a borehole in order to xe2x80x9ccleanxe2x80x9d a clogged formation or may be injected into a borehole in order to seal off a portion of the formation which has become fractured or which is excessively permeable. Sometimes the fluid treatment of boreholes requires the injection of several fluids either simultaneously or in sequence.
One option for performing fluid treatment of boreholes is merely to inject treatment fluids into the borehole from the ground on the assumption that an adequate amount of the fluids will be delivered to their desired location. This option is potentially very expensive, since considerable waste of treatment fluids may result. In addition, where a long section of the borehole must be treated, it may be difficult to deliver adequate amounts of treatment fluids to the desired section of the borehole.
A second option for performing fluid treatment of boreholes is to first isolate the section of the borehole that must be treated with packers or other sealing devices and then inject the treatment fluids only into the isolated section. This option is also potentially very expensive, since the apparatus for isolating the treatment section must be installed in the borehole before the fluid treatment occurs and must be removed from the borehole after the fluid treatment is finished. In addition, if multiple sections or a long continuous section of the borehole must be treated, the isolation apparatus must be moved through the borehole between treatments.
Exemplary apparatus and methods for isolating borehole sections for injection of fluids therein include those described in U.S. Pat. No. 2,764,244 (Page), U.S. Pat. No. 2,869,645 (Chamberlain et al), U.S. Pat. No. 3,319,717 (Chenoweth), U.S. Pat. No. 3,398,796 (Fisher et al), U.S. Pat. No. 3,454,085 (Bostock), U.S. Pat. No. 3,527,302 (Broussard), U.S. Pat. No. 3,945,436 (Nebolsine), U.S. Pat. No. 4,030,545 (Nebolsine), U.S. Pat. No. 4,424,859 (Sims), U.S. Pat. No. 5,002,127 (Dalrymple et al), U.S. Pat. No. 5,018,578 (El Rabaa et al) and U.S. Pat. No. 5,350,018 (Sorem et al).
The apparatus described in the above patents constitute relatively fixed and permanent installations in the borehole which typically require the setting of the sealing devices before fluid injection takes place and the unsetting of the sealing devices after fluid injection is finished in order to facilitate the injection apparatus being removed from or moved within the borehole.
It would be desirable to be able to move the injection apparatus through the borehole without first setting and unsetting the sealing devices since this would undoubtedly result in a saving of time and cost associated with fluid treatment. Unfortunately, none of the patents referred to above appear to contemplate simultaneous fluid injection and movement of the injection apparatus through the borehole.
One explanation for this is that it is difficult to achieve the objective of isolating the section of the borehole into which injection is performed without the use of sealing devices which exert a relatively high sealing force against the interior surface of the borehole, which sealing force is an impediment to movement of the injection apparatus through the borehole.
One attempt to provide an injection apparatus which offers simultaneous fluid injection and movement of the apparatus through the borehole is found in PCT International Publication No. WO 99/34092 (Blok et al), which was published on Jul. 8, 1999.
The Blok apparatus includes a tool which comprises at least three axially spaced swab assemblies which define at least two annular spaces between the tool body and a wellbore. In use the tool is moved through the wellbore while a first treatment fluid is pumped via a first annular space into the wellbore and the formation and a second treatment fluid is pumped via a second annular space into the wellbore and the formation.
The combined effect in Blok of the movement of the tool and the injection of the two treatment fluids is that the first treatment fluid enters the formation before the second treatment fluid so that the two treatment fluids together provide a complete fluid treatment without the need for wellbore cycling to deliver different fluids to the treatment zone separately.
The swab assemblies in Blok are required to satisfy two somewhat incompatible design criteria since they must minimize the amount of sealing force between themselves and the wellbore in order to facilitate movement of the tool through the wellbore and also must provide an xe2x80x9ceffective sealxe2x80x9d between the annular spaces in order to maintain segregation of the treatment fluids in the wellbore before they enter the formation.
In some circumstances, it may be desirable to maintain segregation of fluids after they have entered the formation in addition to maintaining their segregation within the borehole. Blok does not appear to contemplate or address this issue.
One mechanism for maintaining segregation of different fluids in the formation surrounding the borehole is to create an interface between them which restricts their movement in the borehole.
U.S. Pat. No. 4,842,068 (Vercaemer et al) contemplates containing a fluid treatment zone between two protection zones in a wellbore and a formation by simultaneously injecting a treatment fluid into the treatment zone and injecting protection fluids into the protection zones. The interface between the treatment fluid and the protection fluids is created by providing that the protection fluids are immiscible with the treatment fluid. There is no discussion in Vercaemer concerning the pressures or relative pressures at which the treatment fluid and the protection fluids are injected into the wellbore and the formation. There is also no indication in Vercaemer that the method can be performed while moving the injection apparatus through the wellbore.
U.S. Pat. No. 5,002,127 (Dalrymple et al) describes a method for controlling the permeability of an underground well formation by creating a chemical barrier in the formation as an interface between fluids. This chemical barrier is created by simultaneously injecting a first treatment fluid and a second sealant fluid into the formation via a wellbore which is fitted with a packer for maintaining separation of the first fluid and the second fluid in the wellbore. Migration of the second fluid into the portion of the formation occupied by the first fluid is inhibited by substantially balancing the injection pressures of the first fluid and the second fluid. Dalrymple does not contemplate moving the injection apparatus (including the packer) through the wellbore while injection of the first fluid and the second fluid is ongoing.
U.S. Pat. No. 5,018,578 (El Rabaa et al) contemplates the delivery of two separate fluids into two separate zones in a borehole, which zones are separated within the borehole by sealing means such as a packer. The two fluids are chemically reactive with each other such that they form a precipitate which acts as a barrier and interface between the two zones in the formation surrounding the borehole.
Although El Rabaa indicates that the two fluids should be injected into the borehole and the formation sufficient to achieve the stated goal of fracturing the formation in a controlled manner, there is no discussion in El Rabaa concerning the relative pressures at which the two fluids should be injected in order to control the location of the chemical barrier between the two injection zones. Furthermore, El Rabaa does not suggest that the injection apparatus (including the sealing means) can be moved through the wellbore while the two fluids are injected into the wellbore.
It would be advantageous to apply the principles for creating an interface between two fluids to the design of an apparatus which can be moved through a borehole while fluid injection is taking place in order to provide an apparatus which facilitates segregation of different fluids within the borehole while minimizing the design requirements for seals which are included in the apparatus.
The present invention is a method and apparatus for injecting one or more fluids into a borehole in a plurality of zones by creating interfaces in the borehole between zones. The interfaces may be constituted by sealing devices, chemical barriers, physical barriers, pressure balancing between fluids, or by a combination of techniques. Preferably the interfaces are constituted by using a combination of zone interface elements and pressure balancing techniques.
In a method aspect, the invention is a method for injecting an injection fluid into a borehole, the method comprising the following simultaneous steps:
(a) injecting the injection fluid into a primary injection zone in the borehole at an injection fluid pressure, wherein the primary injection zone is bounded longitudinally by a proximal injection zone interface and a distal injection zone interface;
(b) maintaining pressure at the proximal injection zone interface at a proximal interface pressure which is substantially balanced with the injection fluid pressure; and
(c) maintaining pressure at the distal injection zone interface at a distal interface pressure which is substantially balanced with the injection fluid pressure.
The pressure maintaining steps may be performed in any manner which substantially balances the pressures at the injection zone interfaces. Preferably the step of maintaining pressure at the proximal injection zone interface may be comprised of injecting a proximal balancing fluid into a proximal balancing zone in the borehole, wherein the proximal balancing zone is adjacent to the proximal injection zone interface. Preferably the step of maintaining pressure at the distal injection zone interface may be comprised of injecting a distal balancing fluid into a distal balancing zone in the borehole, wherein the distal balancing zone is adjacent to the distal injection zone interface.
The balancing zones may be comprised of a single balancing zone stage or a plurality of balancing zone stages.
Preferably the proximal balancing zone is comprised of a plurality of proximal balancing zone stages disposed sequentially between a proximal end of the proximal balancing zone and the proximal balancing zone interface and the step of maintaining pressure at the proximal injection zone interface is comprised of simultaneously injecting the proximal balancing fluid into each of the proximal balancing zone stages such that a positive pressure gradient is formed from the proximal end of the proximal balancing zone to the proximal injection zone interface.
Preferably the distal balancing zone is comprised of a plurality of distal balancing zone stages disposed sequentially between a distal end of the distal balancing zone and the distal balancing zone interface and the step of maintaining pressure at the distal injection zone interface is comprised of simultaneously injecting the distal balancing fluid into each of the distal balancing zone stages such that a positive pressure gradient is formed from the distal end of the distal balancing zone to the distal injection zone interface.
In the preferred embodiment, each pair of adjacent balancing zone stages is separated by a proximal balancing zone interface. In the preferred embodiment, the proximal balancing fluid has a pressure in each proximal balancing zone stage and the pressure increases between adjacent proximal balancing stages from the proximal end of the proximal balancing zone to the proximal balancing zone interface. In the preferred embodiment, the distal balancing fluid has a pressure in each distal balancing zone stage and the pressure increases between adjacent distal balancing stages from the distal end of the distal balancing zone to the distal balancing zone interface.
Preferably, the method further comprises the step of moving the primary injection zone longitudinally through the borehole while injecting the injection fluid into the primary injection zone and further comprises the step of sensing at least one borehole parameter in the primary injection zone while moving the primary injection zone longitudinally through the borehole.
The step of moving the primary injection zone longitudinally through the borehole may be performed using any apparatus or method. The sensed borehole parameter or parameters may be comprised of any characteristic or property of the borehole or the formation surrounding the borehole, including but not limited to temperature, pressure, permeability, porosity, composition etc. Data pertaining to the sensing of the borehole parameter or parameters may be recorded for analysis at a later date and may be stored with the apparatus performing the method or transmitted for storage outside the borehole.
The proximal balancing fluid and the distal balancing fluid may be comprised of the same fluid or different fluids and the balancing fluids may be different in different balancing zone stages, so long as the pressure maintaining steps can be facilitated. The balancing fluids may be comprised of treatment fluids or may be fluids which serve no purpose other than facilitation of the pressure balancing steps.
In an apparatus aspect, the invention is an apparatus for injecting an injection fluid into a borehole, the apparatus comprising:
(a) a body adapted for passage through the borehole such that an annular space is provided between an outer surface of the body and an inner surface of the borehole;
(b) at least four radially extendable and retractable zone interface elements spaced longitudinally along the body, for filling the annular space between the outer surface of the body and the inner surface of the borehole when extended to define at least three zones along the body;
(c) a zone interface element actuator associated with the zone interface elements for selectively extending and retracting the zone interface elements; and
(d) a fluid delivery system associated with each zone for delivering a fluid to each zone;
wherein the zone interface elements when extended permit the passage of the body through the borehole while inhibiting the fluids from passing between zones.
The fluid delivery system may be comprised of any method or apparatus for delivering fluids to the zones, including but not limited to conduits which are connected with a remote source of fluid or pressurized tanks of fluid associated with the apparatus. Preferably the fluid delivery system is comprised of a plurality of fluid delivery conduits wherein each zone is provided with fluid from at least one fluid delivery conduit. In the preferred embodiment the fluid delivery conduits are carried within the body of the apparatus.
The zone interface element actuator may be comprised of any apparatus or plurality of apparatus which is capable of extending and retracting the zone interface elements. Preferably the zone interface element actuator is comprised of a reciprocating actuator piston which is contained within an actuator chamber. In the preferred embodiment the actuator chamber is carried on the body of the apparatus.
In the preferred embodiment the zone interface element actuator is further comprised of a linkage assembly for operatively linking the actuator piston with the zone interface elements such that reciprocation of the actuator piston will alternately extend and retract the zone interface elements. Preferably the linkage assembly is comprised of a plurality of linkage collars positioned between adjacent zone interface elements for connecting adjacent zone interface elements. Preferably the zone interface elements and the linkage collars are slidably carried on the outer surface of the body of the apparatus. Preferably the fluid delivery conduits communicate with the zones via apertures defined by the linkage collars.
The zone interface elements may be comprised of any apparatus including any structure or device which is capable of extending and retracting and which when extended will provide a zone interface without unduly inhibiting movement of the apparatus through the borehole. The zone interface elements therefore preferably exert only a minimal sealing force against the inner surface of the borehole when they are extended which is sufficient to maintain substantial segregation of fluids between zones when the pressures between zones are substantially balanced.
As a result, the zone interface elements are not comprised of conventional packers or other sealing devices which are designed to maintain a seal between zones where a significant pressure differential exists between zones by exerting a relatively high sealing force against the inner surface of the borehole. Instead, the zone interface elements may be described as xe2x80x9crelatively low pressure sealing devicesxe2x80x9d since they need only provide substantial segregation of fluids in situations where there is a relatively low pressure differential across them.
Preferably the zone interface elements also are not comprised of sealing devices which rely upon significant pressure differentials between zones to provide or enhance their sealing force and thus their sealing capacity. For example, cup type packers or swab assemblies may possibly not be preferred for use as zone interface elements unless they are capable of maintaining substantial segregation of fluids between zones when the pressures between zones are substantially balanced while still permitting relatively uninhibited movement of the apparatus through the borehole when they are extended.
There are therefore two essential criteria for selection of the zone interface elements. First, the total sealing force exerted against the inner surface of the borehole by all of the zone interface elements when they are extended should not unduly inhibit the movement of the apparatus through the borehole. Second, the sealing capacity of each of the zone interface elements should be such that when they are extended they are capable of maintaining substantial segregation of fluids between the injection zone and the balancing zones under the operating conditions of the apparatus. The required sealing capacity of the zone interface elements is controlled by controlling the differential pressure across each of the zone interface elements during use of the apparatus.
In the preferred embodiment, the zone interface elements are comprised of bellows-shaped resilient members which are extended when they are compressed and which are retracted when they are expanded. Preferably the bellows-shaped resilient members provide an outer surface which is gently contoured or rounded when the members are extended in order to facilitate relatively uninhibited movement of the apparatus through the borehole.
The actuator piston is preferably actuated by movement within the actuator chamber under the influence of an actuator fluid. The actuator fluid may be comprised of any gas or liquid and may be the same fluid as any of the injection fluid or the balancing fluids.
Preferably the zone interface element actuator is therefore further comprised of at least one actuator conduit for delivering an actuating fluid to the actuating chamber. Preferably the actuator piston divides the actuator chamber into two sides and preferably the actuator piston is a double acting piston such that the zone interface elememt actuator is comprised of a plurality of actuator conduits for delivering actuator fluid to both sides of the actuator chamber. In the preferred embodiment the actuator conduits are carried within the body of the apparatus.
The fluids and the actuator fluid may be delivered to the zones and the actuator chamber via the fluid delivery conduits and the actuator conduits in any manner. The source of the fluids and the actuator fluid may be located outside of the borehole or inside of the borehole. The source of the fluids and the actuator fluid may also be carried on, in or with the apparatus.
Preferably the source of the fluids is located outside of the borehole and the fluids and the actuator fluid are delivered to the apparatus via the fluid delivery conduits and the actuator conduits via one or more injector devices. Preferably the injector device or devices are located outside of the borehole and are operated from outside of the borehole.
The apparatus is preferably adapted to be moved through the borehole while fluids are being injected into the zones. The apparatus may be moved through the borehole in any manner. In the preferred embodiment the apparatus is connected to a conduit such as a jointed pipe string or coiled tubing string for movement through the borehole. The apparatus may, however, also be configured for connection with a wireline or other suitable conveying system or mechanism. As a result, preferably the apparatus is further comprised of a connector for connecting the apparatus to an apparatus conveying mechanism which is preferably operated from outside of the borehole.